U.S. patent number 4,566,285 [Application Number 06/574,135] was granted by the patent office on 1986-01-28 for refrigerator door ajar alarm with variable delay.
This patent grant is currently assigned to Whirlpool Corporation. Invention is credited to Andrew T. Tershak, Michael D. Thieneman.
United States Patent |
4,566,285 |
Tershak , et al. |
January 28, 1986 |
Refrigerator door ajar alarm with variable delay
Abstract
A door ajar alarm system for a refrigerator-freezer, the system
having a variable alarm delay period. The door ajar alarm system
includes a control which may be digital or analog for monitoring
various operating conditions of the refrigerator such as the
temperatures of the refrigerator compartments and whether the
refrigerator is undergoing a defrost operation. The control
determines the alarm delay period in accordance with the monitored
conditions such that the delay period is decreased in response to
each monitored condition which reaches a predetermined status. The
door ajar alarm thus alerts the user to operating conditions which
are likely to produce an undesirable temperature within the
refrigerator more rapidly than usual or to produce temperatures
from which recovery is unusually slow.
Inventors: |
Tershak; Andrew T. (Center
Township, Vanderburgh County, IN), Thieneman; Michael D.
(Lincoln Township, Berrien County, MI) |
Assignee: |
Whirlpool Corporation (Benton
Harbor, MI)
|
Family
ID: |
24294834 |
Appl.
No.: |
06/574,135 |
Filed: |
January 26, 1984 |
Current U.S.
Class: |
62/129; 340/522;
340/527; 340/585; 374/E3.002; 62/128; 62/131; 62/231 |
Current CPC
Class: |
F25D
29/008 (20130101); G08B 21/18 (20130101); G01K
3/005 (20130101); F25B 2600/23 (20130101); F25D
2700/02 (20130101); F25D 2400/06 (20130101) |
Current International
Class: |
F25D
29/00 (20060101); G01K 3/00 (20060101); G08B
21/18 (20060101); G08B 21/00 (20060101); G01K
013/00 (); F25B 049/00 () |
Field of
Search: |
;340/585,545,527,522,309.15,286R,286M ;200/61.62
;62/125,127,129,126,131 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Refrigerator Alarm", Elektor, vol. 2, No. 11, p. 1141, Nov.
1976..
|
Primary Examiner: Rowland; James L.
Assistant Examiner: Mullen, Jr.; Thomas J.
Attorney, Agent or Firm: Wood, Dalton, Phillips, Mason &
Rowe
Claims
Having described the invention, the embodiments of the invention in
which an exclusive property or privilege is claimed are defined as
follows:
1. In a refrigeration apparatus having means defining a
refrigerated compartment and a door for providing access to said
compartment, an improved door ajar alarm comprising:
means for sensing when said door is open;
means for sensing an operating condition of said refrigeration
apparatus other than the position of said door;
means for providing an alarm; and
control means coupled to said door sensing means, said condition
sensing means and said alarm means for actuating said alarm means
in response to said door being open for a period of time which
varies in accordance with the sensed operating condition of the
refrigeration apparatus.
2. The refrigeration apparatus of claim 1 wherein said control
means includes means for monitoring a plurality of operating
conditions and providing an indication when a monitored condition
reaches a predetermined status, said control means being responsive
to each such indication for determining a door open period which
must elapse before said control means actuates said alarm
means.
3. The refrigeration apparatus of claim 2 wherein said control
means determines a successively shorter period of time for which
the door is to be open in response to each indication that a sensed
condition has reached a predetermined status.
4. In a refrigeration apparatus having means defining a
refrigerated compartment and a door for providing access to said
compartment, an improved door ajar alarm comprising:
means for sensing when said door is open;
a plurality of sensors, each sensor coupled to the refrigeration
apparatus to sense a different operating condition of the apparatus
and to provide a signal representing the sensed condition;
means for providing an alarm; and
control means coupled to said door sensing means, each of said
condition sensors and said alarm means for actuating said alarm
means when said door has been open for a period of time, said
control means including
means responsive to each of said condition sensor signals for
indicating the status of the sensed conditions to provide a
corresponding status signal when a sensed condition reaches a
predetermined status, and
means responsive to said status signals for determining the period
of door open time after which said alarm means is actuated, said
period of door open time being varied thereby in accordance with
the sensed conditions of the refrigeration apparatus.
5. The refrigeration apparatus of claim 4 wherein said determining
means varies the door open period in accordance with the number of
status signals provided.
6. The refrigeration apparatus of claim 4 wherein said determining
means selects successively shorter periods of door open time in
response to each status signal provided.
7. The refrigeration apparatus of claim 4 wherein said control
means comprises a microprocessor control and includes means for
storing said status signals and the determined period of door open
time.
8. The refrigeration apparatus of claim 7 wherein said determining
means varies said period of door open time only when the door is
not open, such that the control means actuates the alarm means when
the door has been open for a period of door open time previously
determined and stored by the control means.
9. The refrigeration apparatus of claim 7 wherein said control
means checks the status of each sensed condition at frequent,
periodic intervals.
10. The refrigeration apparatus of claim 4 wherein at least one of
the sensors is coupled to the refrigeration apparatus to sense the
temperature within the refrigerated compartment, said indicating
means providing a status signal when the sensed temperature is
greater than a reference temperature.
11. The refrigeration apparatus of claim 4 including a defrost
heater, wherein one of said sensors is coupled to the refrigeration
apparatus to sense whether the defrost heater is on or off, said
indicating means providing a status signal when the defrost heater
is on.
12. In a refrigeration apparatus having means defining a
refrigerated compartment and a door for providing access to said
compartment, an improved door ajar alarm comprising:
means for sensing when said door is open to provide a signal which
increases with time when the door is open;
means for sensing the status of a plurality of operating conditions
of the refrigeration apparatus;
means coupled to said sensing means for providing a first reference
signal which varies in response to the status of each operating
condition sensed by the condition sensing means;
means for comparing said door open signal to said reference signal
to provide a trigger signal when the door open signal exceeds the
reference signal; and
means for providing an alarm in response to said trigger
signal.
13. The refrigeration apparatus of claim 12 wherein said means for
providing said reference signal decreases said first reference
signal for each sensed operating condition that reaches a
predetermined status, to thereby decrease the time it takes the
door open signal to exceed the first reference signal.
14. The refrigeration apparatus of claim 12 wherein said sensing
means includes a plurality of sensors, each sensor coupled to the
refrigeration apparatus to sense a different operating condition of
the apparatus and to provide a signal representing the sensed
condition, and said means for providing said first reference signal
includes a plurality of comparators, each comparator coupled to a
different sensor for comparing the condition signal provided by the
sensor to a condition reference signal to provide a status signal
which indicates the existence of a predetermined operating
condition.
15. The refrigeration apparatus of claim 14 further including means
for summing the status signal outputs of each of said comparators
to provide said first reference signal.
16. The refrigeration apparatus of claim 14 wherein one of said
sensors is coupled to the refrigeration apparatus to sense the
temperature of the refrigerated compartment.
17. The refrigeration apparatus of claim 14 including a defrost
heater, wherein one of said sensors is coupled to said defrost
heater to sense whether the defrost heater is on or off.
18. In a refrigeration apparatus having means defining an
above-freezing compartment, a below-freezing compartment, a door
for providing access to said above-freezing compartment, a door for
providing access to said below-freezing compartment, and an
evaporator having defrost heater, an improved door ajar alarm,
comprising:
a temperature sensor arranged to sense the temperature within one
of said compartments;
a defrost sensor arranged to indicate the energization of said
defrost heater;
a first door switch arranged to indicate when said above-freezing
compartment door is open;
a second door switch arranged to indicate when said below-freezing
compartment door is open;
an electrically energizable alarm device for producing an audible
alarm signal; and
a microprocessor-based control for controlling the energization of
said alarm device, comprising:
means for monitoring said temperature sensor and said defrost
sensor and storing signals indicating whether the sensed
temperature is above a predetermined temperature and when the
defrost heater is energized, respectively;
means for establishing a stored count having a value which is
determined by said stored temperature signal and said stored
defrost signal;
means responsive to said first and second door switches and
operative whenever either of said doors has been opened for
terminating the operation of said count establishing means, and
thereafter periodically changing of the value of said stored count;
and,
means for energizing said alarm device when said stored count has
been changed to a predetermined value.
Description
FIELD OF THE INVENTION
This invention relates to an improved door ajar alarm for a
refrigerator-freezer which aids the user in avoiding temperature
conditions within the refrigerator which are deleterious to food
storage.
DESCRIPTION OF THE BACKGROUND ART
Refrigerators having fresh food and freezer compartments have been
known to include a door ajar alarm system for providing an audible
or visual alarm when the door to either of the compartments has
been open for a fixed period of time constituting the alarm delay
period. By thus alerting the user, undesirable temperature
conditions within the compartments may be avoided. It has been
found, however, that the effect of an open compartment door on the
compartment's temperature varies depending on the operating
condition of the refrigerator. Under certain operating conditions
the fixed alarm delay period may be too long so that undesirable
temperature conditions may not be avoided by alerting the user with
known door ajar alarm systems.
One operating condition during which an open compartment door has a
great effect on the compartment's temperature is a defrost
operation. During a defrost operation, defrost heat is being
applied to the evaporator and the compressor cannot be energized to
cool warm air which enters the compartment through an open door, so
that undesirable temperature conditions are rapidly produced. It
is, therefore, desirable to decrease the alarm delay period when
the refrigerator is undergoing a defrost operation. Other operating
conditions under which an open door rapidly produces undesirable
temperatures, or temperature conditions, from which recovery is
unusually slow may occur when either the fresh food or freezer
compartment is at an abnormally high temperature or when the
refrigerator is operating in a special cooling mode, for example,
where the compartments are being cooled to the lowest practical
temperature. Under such operating conditions the fixed alarm delay
period of known systems, though suitable for normal operating
conditions, may be too long to readily alert the user that the door
should be closed.
SUMMARY OF THE INVENTION
In accordance with the present invention, the disadvantages of
prior door ajar alarm systems for refrigerators have been
overcome.
The door ajar alarm system of the present invention monitors
various operating conditions of the refrigerator and varies the
delay period of the door ajar alarm in accordance with the
monitored conditions such that the delay is decreased when a door
is opened during an operating condition which is likely to produce
an undesirable operating temperature within the refrigerator more
rapidly than usual or to produce a temperature condition from which
recovery will be unusually slow.
The door ajar alarm system includes a plurality of sensors, each
coupled to the refrigerator to monitor an operating condition of
the refrigerator, such as the temperatures of the refrigerator
compartments and whether the refrigerator is undergoing a defrost
operation. The system includes a control which is responsive to the
sensor outputs to determine the alarm delay period in accordance
with the sensed operating conditions. The control monitors the
operating conditions as indicated by the sensor outputs and
decreases the alarm delay period for every operating condition
which reaches a predetermined status.
In one embodiment, the control for the door ajar alarm system is
provided by a microprocessor. The microprocessor is responsive to
each of the sensors outputs for monitoring the status of the
operating conditions of the refrigerator, a status signal, or flag,
being provided when a sensed condition reaches a predetermined
status. The microprocessor control determines the alarm delay
period in response to the status signals to vary the delay period
in accordance with the sensed operating conditions of the
refrigerator. The microprocessor control establishes a new alarm
delay period only when the compartment doors are not opened, the
control actuating the alarm once the door has been opened for the
delay period determined by the control immediately prior to the
opening of the door.
In another embodiment, an analog control is provided for the door
ajar alarm system. The analog control is responsive to a
compartment door being opened to provide a signal which increases
with time when the door is open. A comparator compares the door
open signal to a reference signal to trigger an alarm when the door
open signal exceeds the reference signal. The reference signal
applied to the comparator is varied in response to the status of
various operating conditions, as sensed by a plurality of sensors,
the reference signal decreasing in response to each sensed
operating condition reaching a predetermined status. By decreasing
the reference signal, the analog control decreases the delay period
since it takes a shorter time for the door open signal to exceed
the reference signal and thus trigger the alarm.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a refrigerator and the preferred
embodiment of a system for implementing the door ajar alarm control
of the present invention;
FIG. 2 is a flow chart of the main control program of the present
invention;
FIG. 3 is a flow chart of a portion of the main control program to
check the door status and the defrost status of the
refrigerator;
FIG. 4 is a flow chart of a portion of the main control program to
check the refrigerator cooling status and the freezer cooling
status of the refrigerator; and
FIG. 5 is a schematic of the control for the analog door ajar alarm
system of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A door ajar alarm system is shown in FIG. 1 for a refrigerator 10
having a freezer compartment 12 for storing frozen foods and a
compartment 14 for storing fresh foods. The freezer compartment 12
is positioned adjacent a side of the fresh food compartment 14 and
is insulated therefrom by a partition 16. A freezer door 18 and
fresh food door 20 seal off the freezer and fresh food compartments
respectively from the outside.
The fresh food and freezer compartments 14 and 12 are cooled by
passing refrigerated air into the compartments, the air being
refrigerated as a result of being passed in heat exchange
relationship with an evaporator coil 22. Refrigerant flows from a
compressor 24 and a condenser, not shown, through tubing 26 to an
inlet of the evaporator coil 22, the return refrigerant flowing
back to the compressor through tubing connected to the outlet 28 of
the evaporator coil.
A defrost heater 27 is positioned adjacent to the evaporator coil
22 to defrost the refrigerator. The defrost heater 27 may be a
conventional resistive heater energized by means of a relay 29 or
the like under the control of a microprocessor 40. Defrost sensing
means, such as a relay 25 having its coil (not shown) connected in
parallel with the heater 27, are provided to sense whether the
defrost heater 27 is on and to provide a signal indicative thereof
to the microprocessor control 40.
Conventional control means (not shown) may be used to control the
operation of the compressor 24 and the defrost heater 27.
A freezer door switch 30 having a spring loaded actuator 31 is
mounted on the refrigerator cabinet 10 so that the actuator 31 is
compressed by the freezer door 18 when the door is closed.
Similarly, a fresh food door switch 32 having a spring loaded
actuator 33 is mounted on the refrigerator cabinet 10 so that the
actuator 33 is compressed by the fresh food door 20 when the door
is closed. When either of the doors 18 or 20 is opened, the
respective actuator 31, 33 moves outwardly, thereby causing the
contacts of the associated door switch 30, 32 to close. When the
contacts of either of the switches 30, 32 are closed, a signal
indicating that the associated refrigerator compartment door is
open is provided on respective lines 34, 36 to the microprocessor
control 40.
A thermistor 42 positioned within the freezer compartment 12 senses
the freezer temperature and provides a signal representative
thereof on a line 44 to an analog to digital converter 46.
Similarly, a thermistor 48 positioned within the fresh food
compartment 14 senses the compartment temperature and provides a
signal representative thereof on a line 50 to the analog to digital
converter 46. The converter 46 converts the analog signals applied
on lines 44 and 50 to digital signals which are compatible with the
microprocessor control 40.
The microprocessor control 40 is responsive to the temperature
signals from the thermistors 42 and 48 and a signal from the relay
25 indicating that the defrost heater 27 is on, to monitor the
operating conditions of the refrigerator 10 and to determine the
alarm delay period in accordance therewith. The microprocessor 40
actuates an audible alarm 52 by means of a relay 54 when one or
both of the doors has been open for a period of time equal to the
determined alarm delay period. The alarm alerts the user that the
refrigerator door should be closed to avoid temperature conditions
within the refrigerator compartments which are deleterious to food
storage. The microprocessor 40 determines the alarm delay period
for which one of the doors 18 or 20 is to be opened before
actuating the alarm 52, in accordance with the monitored operating
conditions of the refrigerator so as to decrease the delay period
when a monitored operating condition reaches a predetermined
status, as discussed in detail below.
The microprocessor 40 includes a central processing unit or CPU 56
which implements the control logic stored in a read only memory or
ROM 58 in accordance with the data stored in a random access memory
or RAM 60. The RAM 60 includes a number of registers for storing
data input to the microprocessor 40, including a register 62 for
storing the sensed refrigerator temperature, a register 64 for
storing the sensed freezer temperature, an alarm timer register 66
for storing the alarm delay period as determined by the CPU 56 and
registers 68, 70 and 72 for storing respective status signals, or
flags, indicating that the refrigerator and/or freezer temperature
is greater than a desired temperature and that the defrost heater
is on. The microprocessor 40 is also responsive to signals from a
clock 74 which provides a reference for measuring real time
events.
The flow chart shown in FIG. 2 illustrates the main control program
according to which the microprocessor 40 operates to provide the
door ajar alarm. At one second time intervals as determined by a
block 76, the control 40 checks the status of the doors and the
status of the monitored operating conditions of the refrigerator.
The status of the freezer door 18 and the fresh food door 20 are
checked at a block 78 to determine whether one or both of the doors
is open. If neither of the doors is open, the delay period for the
door alarm is determined in accordance with the sensed operating
conditions of the refrigerator. If one or both of the doors is
open, an alarm delay timer is decremented. After checking the door
status, the defrost status is checked by a block 80 to determine
whether the defrost heater 27 is on or not. The cooling status of
the fresh food compartment 14 is then checked by a block 82 after
which the status of the freezer cooling is checked by a block 84.
After performing the last status check at block 84, the control 40
determines whether the one-second check status time interval has
elapsed at block 76, the control waiting until the one-second
period has elapsed before performing the next status check.
Upon entering the door status check at block 78, as shown in FIG.
3, the control 40 first determines whether one of the doors 18 or
20 is open at a block 86. If neither of the doors is open, the
control 40 determines the alarm delay period as follows. At a block
88 an inquiry is made as to whether the refrigerator
overtemperature flag is set, indicating that the fresh food
compartment temperature is above a predetermined level. If the
refrigerator overtemperature flag is not set, an inquiry is made at
block 90 to determine whether the freezer overtemperature flag is
set, indicating that the freezer is above a predetermined level. lf
the freezer overtemperature flag is not set, the control 40 at a
block 92 determines whether the defrost flag has been set
indicating that the defrost heater is on. If it is determined by
blocks 88, 90 and 92 that none of the flags have been set, the door
alarm timer 66 is set to 180 seconds by a block 94.
If neither the refrigerator overtemperature flag nor the freezer
overtemperature flag is set as determined by blocks 88 and 90, but
the defrost flag is set as determined by block 92, a block 96 sets
the door alarm timer to 90 seconds. If it is determined at block 90
that the freezer overtemperature flag is set but at blocks 88 and
98 it is determined that neither of the refrigerator or defrost
flags is set, the door alarm timer is also set to 90 seconds by the
block 96. Similarly, if at block 88 it is determined that the
refrigerator overtemperature flag is set, but a block 100
determines that the freezer overtemperature flag is not set and a
block 102 determines that the defrost flag is not set, the block 96
sets the door alarm timer to 90 seconds.
From the above, it is seen that the delay period for the door alarm
timer is decreased from 180 seconds to 90 seconds if one of the
monitored operating conditions reaches a predetermined status as
indicated by a set flag. That is, the door alarm timer is set to 90
seconds by the block 96 when only one of the flags, the
refrigerator overtemperature flag, the freezer overtemperature
flag, or the defrost flag, is set.
A block 104 sets the door alarm timer to 60 seconds if it is
determined by block 88 that the refrigerator overtemperature flag
is not set, but the freezer overtemperature flag and the defrost
flag are set, as determined by blocks 90 and 98. The block 104 also
sets the door alarm timer to 60 seconds when the block 88
determines that the refrigerator overtemperature flag is set, the
block 100 determines that the freezer overtemperature flag is not
set, and the block 102 determines that the defrost flag is set.
Further, if the refrigerator overtemperature flag is set as
determined by block 88, and the freezer overtemperature flag is set
as determined by block 100, but the defrost flag is not set as
determined by a block 106, the block 104 sets the open door alarm
timer to 60 seconds.
It is seen from the above that the delay period for the door alarm
timer is further decreased if two monitored operating conditions
reach a predetermined status. That is, when the control 40
determines that two of the flags are set, the door alarm timer is
set to 60 seconds. If all three flags are set, indicating that the
refrigerator compartment is overtemperature as determined by block
88, the freezer compartment is overtemperature as indicated by
block 100, and the defrost heater is on as indicated by block 106,
a block 108 sets the door alarm timer to 45 seconds to further
decrease the delay period.
The delay period for the door alarm timer is set only when neither
of the refrigerator compartment doors 18 or 20 is open. If one of
the doors is open as determined by block 86, the open door alarm
timer as previously set is decremented by one second by a block
110. After decrementing the alarm timer, a block 112 determines
whether the alarm timer has been decremented to zero. If the alarm
timer has been decremented to zero, a block 114 actuates the
audible alarm 52 through the relay 54. If the alarm timer has not
been decremented to zero as determined by block 112, the control
proceeds to check the defrost status at block 80.
In checking the status of the defrost at block 80, a block 116
determines whether the defrost heater is on by checking to see
whether there is a signal from the relay 25 applied to the
microprocessor 40. If the block 116 determines that the defrost
heater is on, a defrost flag is set by a block 118. If it is
determined that the defrost heater is not on, the defrost flag
stored in the register 72 is reset by a block 120. After setting or
resetting the defrost flag at blocks 118 or 120, the status of the
refrigerator cooling is checked at block 82 as shown in FIG. 4.
In order to monitor the status of the refrigerator cooling at block
82, a block 122 reads the fresh food compartment temperature stored
in the register 62 of the RAM 60. A block 124 determines whether
the fresh food temperature read at block 122 is over a
predetermined level and, if it is, a block 126 sets the
refrigerator overtemperature flag in the register 68. If the fresh
food compartment is not overtemperature, a block 128 resets the
refrigerator overtemperature flag in the register 68. The control
then continues the status check at block 84.
At block 84, in order to check the status of the freezer cooling,
the freezer temperature stored in the register 64 of the RAM 60 is
read by a block 130. A block 132 determines whether the freezer
temperature as read by block 130 is over a predetermined level and,
if it is, a block 134 sets a freezer overtemperature flag in the
register 70 of the RAM 60. If it is determined that the freezer
compartment is not over temperature, a block 136 resets the freezer
overtemperature flag in the register 70 and the program exits to
point A to determine whether the one-second check status time
interval is up at block 76.
From the above it is seen that the microprocessor control 40
provides a variable door ajar alarm delay wherein an appropriate
delay period is determined by the control 40 in response to the
status of the monitored operating conditions of the refrigeration
apparatus 10. The alarm delay period is set to a decreased value
whenever an operating condition reaches a status which is likely to
more rapidly produce an undesirable operating temperature within
the refrigerator or to produce a temperature condition from which
recovery will be unusually slow. It is noted that operating
conditions of the refrigerator 10 other than the
refrigerator-freezer temperature and defrost operation may be
monitored by the door ajar alarm system of the present invention
and an appropriate delay period determined by the microprocessor 40
in response thereto.
In a second embodiment of the door ajar alarm system of the present
invention, an analog control means is provided, as shown in FIG. 5.
The door ajar alarm system includes a pair of normally closed door
switches 140 and 142, the switches 140, 142 associated with the
freezer door 18 and the fresh food door 20 respectively. The door
switches 140 and 142 are coupled to the noninverting input terminal
144 of a comparator 146 through a 100.OMEGA. resistor 148 and a
series combination of a 5.1 M.OMEGA. resistor 150 and a 50 .mu.f
capacitor 152 connected between +5 volts and ground. When one of
the door switches 140 or 142 is open, indicating that a
refrigerator compartment door 18 or 20 is open, the voltage applied
to the terminal 144 of the comparator 146 increases with time
during the time that the door is open as illustrated by the graph
154.
The "door open" signal applied to the terminal 144 is compared by
the comparator 146 to a reference signal applied to the inverting
input terminal 156 thereof. The output of the comparator on a line
158 goes high when the door open signal exceeds the reference
signal applied to the terminal 156. A high signal output from the
comparator on line 158 triggers a timer 160, which may be a LM 555
timer manufactured by National Semiconductor Corporation. When
actuated, the timer 160 energizes a piezoelectric transducer alarm
or piezo-alarm 162 to audibly alert the user that the refrigerator
door has been opened for a period of time determined by the
crossover point of the door open signal and the reference
signal.
The reference signal applied to the terminal 156 of the comparator
146 is varied according to the operating conditions of the
refrigerator as sensed by the thermistors 42 and 48 and by a reed
switch 164 which is responsive to the defrost heater as discussed
below. The freezer thermistor 42 is connected between +5 volts and
a 90.9 K.OMEGA..+-.1% resistor 166 which is connected to ground,
the thermistor 42 also being connected to an inverting input
terminal 167 of a comparator 168. The fresh food compartment
thermistor 48 is connected between +5 volts and a 40.2
K.OMEGA..+-.1% resistor 170 which is connected to ground, the
thermistor 48 also being connected to an inverting input terminal
171 of a comparator 172. The thermistors 42 and 48 are weighted so
that the outputs of each may be compared to the same reference
signal applied to the noninverting input terminals 174 and 176 of
the respective comparators 168 and 172 to cause the output of the
comparator 168 to go low when the freezer is overtemperature and to
cause the output of the comparator 172 to go low when the fresh
food compartment is overtemperature. The reference signal applied
to terminals 174 and 176 is provided by a voltage divider comprised
of a 100 K.OMEGA. resistor 178 and a 100 K.OMEGA. resistor 180
connected in series between +5 volts and ground. When the signal
applied to the terminal 171 exceeds the signal applied to the
terminal 176 the output of the comparator 172 goes low indicating
that the fresh food compartment is overtemperature. Similarly, when
the signal applied to the terminal 167 exceeds the signal applied
to the terminal 174, the output of the comparator 168 goes low,
indicating that the freezer compartment is overtemperature.
In order to determine whether the refrigerator 10 is undergoing a
defrost operation, the reed switch 164 is provided. The switch 164
closes in response to magnetic flux produced by current flowing
through the wire 182 which supplies power to the defrost heater 27,
indicating that the defrost heater is on. When the defrost heater
is on, the magnetic flux causes the switch 164 to open and close in
response to the cycles of the 60 Hz alternating current, producing
a pulse train on a line 184 which is applied to a 100.OMEGA.
resistor 186. The pulse train on line 184 is filtered by a parallel
combination of a 100 K.OMEGA. resistor 188 and a 0.47 .mu.f
capacitor 190 to provide a DC signal which is applied to the
inverting input terminal 192 of a comparator 194. The signal
applied to the terminal 192 of the comparator 194 is compared to
the reference signal generated by the voltage divider 196 which is
applied to the noninverting input terminal of the comparator. When
the defrost heater is on, the signal on line 192 exceeds the
reference signal applied to the terminal 198 causing the output of
the comparator 194 to go low.
The variable reference voltage applied to the terminal 156 of the
comparator 146 is determined by summation of the outputs of the
comparators 168, 172, 194 and a voltage divider 200 at a summing
junction 202, the comparators 168, 172 and 194 each being coupled
to the junction 202 through a respective 6.8 K.OMEGA. resistor 204,
206 and 208. The voltage divider 200 is comprised of an 8.2
K.OMEGA. resistor 210 connected in series with a 10 K.OMEGA.
resistor 212 between +5 volts and ground.
The outputs of each of the comparators 168, 172 and 194 can be
viewed as status signals similar to the status signals or flags
stored in registers 70, 68 and 72 of the first embodiment.
When none of the monitored operating conditions have reached a
predetermined status, the output of each of the comparators 168,
172 and 194 is high. When the high outputs of the comparators are
summed with the output of the voltage divider 200, a reference
signal is provided which will be exceeded by the open door signal
applied to the terminal 144 after an alarm delay period of 180
seconds. If one of the monitored operating conditions reaches a
predetermined status such that either the fresh food compartment or
freezer compartment is overtemperature or the refrigerator is
undergoing a defrost operation, the respective comparator 168, 172
or 194 goes low, decreasing the reference voltage applied to the
terminal 156 of the comparator 146. The reference voltage applied
to the terminal 156 when only one of the operating conditions has
reached its predetermined status is such that the door open signal
applied to the terminal 144 exceeds the reference signal after an
alarm delay period of 90 seconds. If two of the monitored operating
conditions reach their predetermined status, indicated by two of
the comparator outputs going low, the reference voltage applied to
the terminal 156 of the comparator 146 is such that the open door
signal applied to the terminal 144 exceeds the reference signal
after an alarm delay period of 60 seconds. If all three of the
monitored operating conditions have reached their predetermined
status, indicated by low outputs from all three of the comparators
168, 172 and 194, the voltage divider 200 establishes the reference
voltage applied to the terminal 156, the reference voltage being
such that the door open signal exceeds the reference signal after
an alarm delay period of 45 seconds.
The door ajar alarm system of the present invention having a
variable alarm delay period provides an adequate warning for the
user under various operating conditions of the refrigerator. The
alarm delay period for the system is set to successively shorter
periods of time for each operating condition which reaches a
predetermined status so that the alarm is always actuated before
undesirable temperature conditions are reached.
* * * * *